This invention relates to methods and compositions for inhibiting the air oxidation and spontaneous combustion of coal, low-ranked coal, and in particular sub-bituminous coal. Sub-bituminous coal forms within fresh water peat bogs that do not get washed out into the sea and therefore have unique chemical properties. Due to the differences in its formation, sub-bituminous coal has a loose pore structure and retains high levels of water. As a result it is a less efficient fuel than other coals such as anthracite or bituminous coal, and can require as much as double the amount of coal mass to produce the same amount of energy. Sub-bituminous coal also contains large pyrite particles which tend to foul and slag furnace walls before they completely combust. It is not surprising then that historically, sub-bituminous coal has been recognized to be a lower value, less desired feedstock fuel for power generation.
Although all coal dust poses a risk of an airborne explosion, low-ranked and especially sub-bituminous coal poses additional fire risks even when not-in the form of airborne dust. Low-ranked coals are potentially more prone to particle degradation, thereby increasing the open surface area. This facilitates oxidation which can lead to spontaneous combustion. It is believed that, the autogenous grinding tendencies of shipping, handling and transfer of low-ranked coal creates increasingly small particles, increased surface area, and a rich environment for air oxidation to occur resulting in the potential for spontaneous combustion of that coal.
As a result, as mentioned for example in the article Fire-protection guidelines for handling and storing PRB coal, by Edward B. Douberly, Power Magazine (October 2003), special handling procedures must typically be employed by those low-ranked coal users to decrease the risk of unwanted fires but these procedures make it difficult to simply replace other higher rank coals with low-ranked coal as a substitute fuel in coal based power generation. Low-rank coal users strive to minimize the time allowed to elapse between the mining and ultimate burning of sub-bituminous coal. Furthermore when received at its destination, the coal inventory must be tightly managed, piles groomed to minimize surface area and organized in a FIFO manner such that the age-order of coal inventory forces utilization of the “oldest inventory” first. Also, feeding and handling machinery must be specially designed to minimize attrition and aggressive handling lest coal particle size continue to degrade, allowing finer and finer fragments to turn to dust, accumulate and spontaneously combust. Finally, thermal and atmospheric detectors are employed to constantly analyze piles for the telltale signs of the early stages of spontaneous combustion which must then be rapidly treated or consumed for power production to prevent further degradation.
These degradation processes present an even greater risk in overseas transport of low-rank coal. Most US harbor facilities, let alone foreign ones, lack the special handling equipment needed to safely handle low-rank coal. In addition the coal placed in a ship's hold for extended periods of time creates a situation in which the risk of combustion is intolerably high.
The relatively lower Btu value as well as the increased risk of fire or have, for much of the history of the coal fired power industry, caused sub-bituminous coal to be removed from contention as a useful alternative to higher rank coals.
Recently, however, increasing anthracite and bituminous coal mining costs and rising environmental standards have changed the relative value of sub-bituminous and low-ranked coal. Helping to offset the higher moisture content are sub-bituminous coals' far lower levels of undesirable constituents such as sulfur, mercury or arsenic. Also, subbituminous coal's high Calcium. Oxide and Magnesium Oxide levels cause sub-bituminous coal combustion to produce far less boiler slag. As a result, despite its lower inherent energy and handling difficulties, in many jurisdictions strict environmental laws have made it more suitable to use sub-bituminous coal than other sources of coal, even though they might be of higher fuel content. As a result, sub-bituminous coal tonnage has greatly increased over the past decade and subbituminous coal producers are actively seeking methods for safe shipment in massive ocean-going vessels and acknowledge the urgent need for technology to address the dangers in spontaneous combustion of this coal.
Thus there is a clear utility in novel methods and compositions for inhibiting the spontaneous combustion of coal piles. The art described in this section is not intended to constitute an admission that any patent, publication or other information referred to herein is “Prior Art” with respect to this invention, unless specifically designated as such. In addition, this section should not be construed to mean that a search has been made or that no other pertinent information as defined in 37 CFR §1.56(a) exists.